.. _kbcomponent:

KBComponent
===========

Background
----------

In order to understand the design of the knowledge base component of the ELTK, we provide a brief explanation of how data and ontologies are used within knowledge engineering, especially in the context of `Description Logics <http://dl.kr.org/>`_ and related languages such as the Web Ontology Language (OWL). Knowledge bases in the Description Logic world consist of two logically separate components: 

    * the ontology proper (called the TBox) 
    * the various assertions about concepts from the ontology (called the ABox) 
      
So, the standard description of such a knowledge base (KB) is  KB = <TBox, ABox>, where TBox is a set of classes and relations and ABox is a set of assertions about instances of classes.  For example, the fact that ``all syntactic words are syntactic units`` belongs to the TBox. But some bit of knowledge, e.g., the formula describing that a particular syntactic word has a particular prefix, belongs in the ABox. Furthermore, since we're dealing with `Linked Data <http://linkeddata.org>`_, the situation is a bit more complex. Namely, the TBox-ABox distinction is muddied since both sorts of statements can exist in a single Linked Data resource. To capture the mixing of TBox and ABox, we use the notion of a "KB component", which can contain either type. It can also contain TBox statements from different ontologies. This kind of assumption is built in to the RDF, Semantic Web architecture.

Chunks of knowledge
--------------------

.. automodule:: eltk.kb.KBComponent

.. autoclass:: eltk.kb.KBComponent.KBComponent

.. .. automethod:: eltk.kb.Ontology.Ontology.__init__(self,identifier='')

.. .. automethod:: eltk.kb.Ontology.Ontology.parse(self, source, publicID=None, format="xml")

.. .. automethod:: eltk.kb.Ontology.Ontology.addEntity(self,ent)

.. Access methods
.. --------------

.. Ontology has several methods to access its data:

.. .. automethod:: eltk.kb.Ontology.Ontology.getClasses(self)

..  .. automethod:: eltk.kb.Ontology.Ontology.getObjProp(self)

..  .. automethod:: eltk.kb.Ontology.Ontology.getDatatypeProp(self)

..  .. automethod:: eltk.kb.Ontology.Ontology.getIndividuals(self)

..  .. automethod:: eltk.kb.Ontology.Ontology.getEntity(self,uri)



Illustration of usage
---------------------

Here's how to create a knowledge base component: ::

    >>> from eltk.kb.KBComponent import KBComponent
    >>> from eltk.kb.Meta import *

Create the KBComponent, and then some classes and properties: :: 

    >>> mykb = KBComponent(URIRef('http://foo.org/myid'))
    >>> Word = Meta.OWLClass.new(u'http://blah.org/Word')
    >>> w = Word(u'w')
    >>> hasConstituent = Meta.OWLObjectProperty.new(u'http://purl.org/linguistics/gold#hasConstituent')
    >>> Morpheme = Meta.OWLClass.new(u'http://blah.org/Morpheme')
    >>> m1 = Morpheme(u'http://blah.org/m1')
    >>> m2 = Morpheme(u'http://purl.org/linguistics/gold#m2')

And add a statement to the KBComponent: ::

    >>> mykb += (w, hasConstituent, m1)

The statement is in the form of a triple, and is equivalent to this: ::

    >>> mykb += hasConstituent(w, m1)

See :doc:`meta` for an explanation of how particular instances of classes and properties are created.


.. Ontology
.. --------

.. .. autoclass:: eltk.kb.KBComponent.Ontology


Methods
-------

Here are the methods associated with KBComponent.

.. automethod:: eltk.kb.KBComponent.KBComponent.getOWLClasses

.. automethod:: eltk.kb.KBComponent.KBComponent.buildRDFGraph

.. automethod:: eltk.kb.KBComponent.KBComponent.getTermMeaning

.. automethod:: eltk.kb.KBComponent.KBComponent.renderJSON



Depending on the contents of a particular :class:`KBComponent`, several methods could be applicable.